Abstract
Inducer is often used to improve the cavitation performance of pump. In order to study the cavitation characteristics of inducer under low flow condition of high-speed pump, high-speed photography technology was employed in this paper to carry out visual experiments on the inducer of a high-speed centrifugal pump. In low flow rates, Cavitation distribution and evolution among the inducer were captured. The experimental results revealed that a band-shaped backflow vortex in the inlet pipe would occur when the flow rate was less than 0.3 Qd. Moreover, the backflow vortex in the inlet pipe rotated with the inducer and the rotational speed of backflow vortex was approximately half of the inducer. The visualization test of 0.27 Qd was carried out: when the NPSH was greater than 6.72 m, the bubbles in the inlet pipe were asymmetrical; When the NPSH dropped to 5.41 m, the cavitation was becoming less asymmetrical; When NPSH dropped to 3.81 m, cavitation evolved to the deteriorating stage, plenty of bubbles entered into the main impeller, resulting in a rapid decline of pump performance. Furthermore, the cavitation performance was worse at an extreme flow rate, and the NPSH value of 0.27 Qd was 7.5% greater than that under design condition.
Highlights
Cavitation causes a decrease in the performance of the centrifugal pump, which is an explicit affection to the high-speed centrifugal pump
When the magnetic drive pump was operating under low flow condition, a long band-shaped backflow vortex appeared in the inlet pipe which went from the inlet pipe band-shaped backflow vortex appeared in the inlet pipe which went from the inlet pipe to the leading edge of the inducer blade
Backflow vortex only existed at the leading edge of the inducer, which indicated that the backflow vortex diffused to the upstream significantly when pump operated at low flow rate
Summary
Cavitation causes a decrease in the performance of the centrifugal pump, which is an explicit affection to the high-speed centrifugal pump. The results show that cavitation has a minor effect on static pressure distribution, and a larger tip clearance leads to an increase in the tip leakage vortex cavitation This type of cavitation causes the pump head to drop rapidly when the NPSH is relatively small. Tsujimoto et al [14] have employed high-speed photography to capture the backflow vortex cavitation phenomenon of the inducer under the design condition. The results show that when the pump operates at designed conditions, the backflow vortex disappears at the leading edge when the inlet pressure reduces further. Based on the visual experiment results, the cavitation evolution under low flow conditions, asymmetric cavitation phenomenon in the inducer, and the effect of cavitation on the pump performance were well-analyzed
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